ESTRO 2021 Abstract Book

S154

ESTRO 2021

25.8 +/- 5.1 in controls, p=0.02). Conclusion

Impaired QoL persists over years in breast cancer survivors treated with RT, in particular in patients younger than 65 years, and may be partly attributable to the breast cancer disease and/or its treatment. Potential impairment in QoL may require greater attention in follow-up care after treatment.

PH-0221 Invasive ductal carcinoma tumor grade in patients treated with intra-operative radiation therapy B. Schwartzberg 1 , H. Chang 2 , A.M.N. Syed 3 , W. Hodge 4 , S. Reiner 5 1 Schwartzberg Center for Minimally Invasive Breast Surgery, Department of Surgery, Santa Rosa, USA; 2 David Geffen School of Medicine at UCLA, Department of Surgery, Los Angeles, USA; 3 Long Beach Medical Center, Department of Radiation Oncology and Endocurietherapy, Long Beach, USA; 4 Advent Health Florida Hospital, Department of Radiation Oncology, Orlando, USA; 5 Swedish Medical Center, Department of Radiation Oncology, Englewood, USA Purpose or Objective An institutional review board-approved single arm prospective non-randomized multi-institution trial, the ExBRT trial, was designed to determine the efficacy and outcome of single fraction intra-operative radiation therapy (IORT) at the time of breast conserving surgery for early-stage breast cancer. This trial included women age > 40 years with biopsy proven SBR Grade I, II and III invasive ductal carcinoma (IDC) < 30 mm by pre-operative clinical and radiographic evaluation. Preliminary results of these 3 patient (pt) SBR Grade Between May 2012 – July 2018, 922 enrolled pts with pre-operative IDC were successfully treated per protocol with lumpectomy plus single 20 Gy fraction IORT using disposable balloon electronic brachytherapy. Negative margins and cancer free lymph nodes were required on final pathology. Local standards of care guided adjuvant medical therapy. Follow-up was at 6, 12, and 18 months then yearly. Data collection included demographics, histopathology, margins, prognostic factors, medical therapy, local recurrence (LR), and survival. The Exact Chi-square, 2 sided test was used for statistical analysis. Results 922 pts (aged 41 - 93, mean 66.4 years) with biopsy-proven IDC completed IORT treatment per protocol. Median follow-up was 4 years. Mean IDC size on final pathology was 11.7 mm (range 0.03 – 70 mm). Estrogen receptor status was positive in 743 (96%) of the 778 pts for which it was available. 854 (93%) of the 922 pts were post-menopausal. Histologic tumor grade subsets were as follows: Grade I: 374 (40.6%) pts, Grade II: 429 (46.5%) pts, and Grade III: 119 (12.9%) pts. There was no breast cancer related death. There were 31 (3.4%) LR (mean age 66 years, mean size 13.7 mm, range 4 – 30 mm). In the Grade I subset, there were 8 LR (mean age 66.5 years, mean size 11.8 mm) for a subset recurrence rate of 2.1%. There were 14 (3.3%) LR (mean age 65.2 years, mean size 14.1 mm) in the Grade II subset. There were 9 (7.6%) LR (mean age 67.3 years, mean size 14.9 mm) in the Grade III subset. Recurrences in the Grade III pt subset did not reach statistical significance At median follow-up of 4 years, 922 IDC pts successfully treated with single 20 Gy fraction IORT per protocol using disposable balloon electronic brachytherapy in the ExBRT trial were found to have a recurrence rate of 3.4%. Although SBR Grade III tumors were found to have a higher recurrence rate, this did not reach statistical significance. The recurrence rates observed in this trial are similar to those reported in the prospective randomized TARGIT-A trial, which differs in that TARGIT-A is a risk-adjusted trial with only 80% of reported pts receiving single fraction IORT for treatment. The recurrence rates in this ExBRT trial are comparable to single- arm peer-reviewed IORT published data and traditional IDC treatments using breast conserving surgery plus whole breast radiation therapy. subsets were analyzed Materials and Methods (p=0.0439). Conclusion PH-0222 Irradiation With or Without Boost in Low Risk Early Breast Cancer: Data from a Large Health System S.W. Seol 1 , T. Pflederer 2 , L. Weller 3 , C. Goodman 4 , E. Donnelly 1 , J. Hayes 1 , J. Strauss 1 1 Northwestern University Feinberg School of Medicine, Department of Radiation Oncology, Chicago, USA; 2 University of Illinois at Chicago, College of Medicine, Chicago, USA; 3 Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, USA; 4 MD Anderson Cancer Center, Department of Radiation Oncology, Chicago, USA Purpose or Objective Patterns-of-failure data identify most in-breast recurrences as located near the lumpectomy bed, supporting the role of targeted dose escalation: a “boost”. Two randomized trials found a loco-regional control (LRC) benefit for the boost that outweighs its modest increases in fibrosis and telangiectasia. However, subset analyses have shown a smaller absolute benefit in women over age 50 and in those with grade 1-2 histology. These findings harmonize with an analysis of the IMPORT Low trial, in which patients across all arms received 40.05Gy in 15 fractions to the lumpectomy bed without a boost. In patients with no high risk factors (age 50, grade 1-2, ER+, HER2-, LVI-, margin -), the five year rate of LRC was 99%, whereas it was 95% for patients with one or more risk factors. These data suggest that a boost would bring little benefit to this low risk population. This analysis reports on outcomes of patients with low risk early breast cancer treated with EBRT at a multi- hospital health system. We hypothesized that the addition of a boost would not be associated with a benefit in

LRC in this population. Materials and Methods

The shared electronic health record of multiple facilities within a university health system was queried to identify women with pathologic T1-2 N0 breast cancer treated with breast-conserving surgery between 2007